Panels (usually square) of pressed steel have been long used for making water storage tanks, the earliest known patent being the British patent having the specification No. 22900 of 1901 in the name of George Herbert Lloyd.
Very little change in the manufacture of such panels and tanks has occurred since.
Such panels are not capable of being used for making any structure other than tanks. Furthermore, such panels are made with accurately square corners and are fitted together without auxiliary members to make a tank. Several separate manufacturing stages are necessary to make such known panels including pressing hot steel blanks in a press and machining or grinding the edges and corners.
Improved tanks can be made according to the invention which especially finds realisation where modern materials such as reinforced plastic material is used in the manufacture of the panels.
The panels are superior both mechanically and aesthetically; and so are tanks made from them.
The panels can be made by a one-step method such as hot press moulding.
A theoretical proposal, not put into practice, is contained in British patent specification No. 1390176.
That proposal is for panels made by hand laying-up of glass-reinforced material. Stiffening of the panels is proposed by layer overlaps formed during laying up.
Such panels are not relieved at the corners and could not be made by moulding techniques because the sharp corners would not be correctly formed during the moulding process. The moulding process requires flow of material during moulding but adequate flow cannot occur at sharp corners of the kind shown in British specification No. 1390176.
Furthermore, the tank proposed in British Pat. No. 1390176 has no bracing to reinforce the tank walls and its walls are apparently liable to buckle under pressure from contained water.
It is in fact not possible to construct a tank in which forces due to pressure of contained liquid are sustained by the walls entirely free of bracing because the forces are too great.
A further theoretical proposal is given in British patent specification No. 1174893 in which tank panels are proposed to be made by extrusion. Each panel is to have an inner-facing layer of thermoplastic material bonded to the panel surface and the layers of adjacent panels being bonded at their edges to one another to form a continuous sealing layer within the tank.
Such a proposal is extremely impractical and would involve prohibitive costs of manufacturing of panels and erection of tanks.
The prior proposals have not led to panels or tanks being made and put into effective use.
Tanks according to the present invention have been made by the assignee of the present inventor. Said assignee is a principal manufacturer and exporter of pressed steel tank panels and is about to market tanks made according to the invention.